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QUANTITATIVE  ESTIMATION

water, which gives a result free from any error arising from incorrect
vapour tension. The manner of transferring the gas is shown in
Fig. 16. The stem of a wide funnel is cut off and attached by rubber
to the top- of the azotometer. This is then filled with water and the
projecting end of the azotometer is also filled with water. A graduated
tube is now brought over the end, and by opening the tap and raising



FIG. 16.

the reservoir the gas passes into the tube.    The end is now closed with
the thumb and transferred to a cylinder of water.
The tube is held by a collar of paper, whilst the level is adjusted
and the volume and temperature noted.
Before commencing a second determination, the contents of
the combustion tube are emptied on to the wire-gauze sieve,
placed over one of the tin dishes, and the fine and coarse oxide
separated. Both oxides are roasted in order to reoxidise any
reduced copper, and transferred as before to their respective
flasks. The sodium bicarbonate tube is emptied into, a special
C   2